The invention relates to a method for operating an internal combustion engine, especially of a motor vehicle, wherein fuel is injected into the combustion chamber in a first operating mode during a compression phase and in a second operating mode during an induction phase. In the method, the exhaust gas is supplied to a catalytic converter and exhaust gas is recirculated. The invention likewise relates to a corresponding internal combustion engine as well as a corresponding control apparatus for an engine of this kind.
A method of this kind, an internal combustion engine of this kind and a control apparatus of this kind are all, for example, known from a so-called gasoline direct injection. There, fuel is injected into the combustion chamber of the engine in a homogeneous operation during the induction phase or in a stratified operation during the compression phase. The homogeneous operation is preferably provided for the full-load operation of the engine; whereas, the stratified operation is suitable for idle operation and part-load operation.
The internal combustion engine is operated with an excess of air especially in the stratified operation. This can lead to high temperatures of the exhaust gas. Likewise, in stratified operation, it is necessary that the exhaust gas is intermediately stored with the aid of an NOx storage catalytic converter in order to thereafter reduce the exhaust gas by a three-way catalytic converter. However, for the operation of the NOx storage catalytic converter, the temperature thereof may not exceed a specific limit temperature. The toxic substances contained in the exhaust gas increase when the limit temperature is exceeded.
It is an object of the invention to provide a method for operating an internal combustion engine with which the toxic substances in the exhaust gas are reliably held to a lowest possible level.
This task is solved with a method of the kind mentioned initially herein in accordance with the invention in that the exhaust-gas recirculation rate of the exhaust-gas recirculation is controlled (open loop and/or closed loop), inter alia, in dependence upon the temperature of the catalytic converter. The object is solved in accordance with the invention in an internal combustion engine and a control apparatus of the type mentioned initially herein.
The temperature of the catalytic converter can be reduced or increased by correspondingly influencing the exhaust-gas recirculation rate. This is utilized in the temperature-dependent influencing of the exhaust-gas recirculation rate in accordance with the invention in that the temperature of the catalytic converter is held below the limit temperature.
The mass flow through the engine and therefore the thermal flow in the exhaust-gas system can be reduced via the exhaust-gas recirculation. This defines a cooling of the exhaust-gas system. Low temperatures in the combustion chamber of the engine arise with the exhaust-gas recirculation essentially because of the later combustion based on a slower speed of the flame front in the combustion chamber.
According to the invention, especially more exhaust gas is recirculated with increasing temperature. This has the consequence that the air excess in the intake manifold is reduced in correspondence to the quantity of the recirculated exhaust gas. This, in turn, has the consequence that the temperature in the combustion chamber becomes less. From this, a lower temperature of the exhaust gas, and therefore of the catalytic converter, results. The temperature of the catalytic converter is thereby reduced because of the increased recirculation of exhaust gas because of the increasing temperature.
In total, it is ensured that the temperature of the catalytic converter remains below the limit temperature and therefore an optimal operation especially of the NOx storage catalytic converter is possible.
In especially advantageous embodiments of the invention, the temperature of the catalytic converter is measured and/or the temperature of the catalytic converter is derived from a temperature of the exhaust gas and/or the temperature of the catalytic converter is modeled.
In a further advantageous embodiment of the invention, the exhaust-gas recirculation is controlled (open loop and/or closed loop) in dependence upon a rough running. In this way, it is possible to consider the rough running as a limit for the control (open loop and/or closed loop) of the exhaust-gas recirculation rate.
Of special significance is the realization of the method of the invention in the form of a control element which is provided for a control apparatus of an engine, especially of a motor vehicle. A program is stored on the control element which is capable of being run on a computer, especially on a microprocessor, and is suitable for executing the method according to the invention. In this case, the invention is realized by a program stored on the control element so that this control element, which is provided with the program, defines the invention in the same way as the method which the program can carry out. Especially an electric storage medium can be used as a control element, for example, a read-only-memory or a flash memory.
Further features, application possibilities and advantages of the invention will become apparent from the following description of embodiments of the invention which are illustrated in the drawing. All described or illustrated features define the subject matter of the invention by themselves or in any desired combination independently of their summary in the patent claims or their dependency as well as independently of their formulation or presentation in the description and/or in the drawing.